代码如下：

            try
            {
                HttpWebRequest httpReq = (HttpWebRequest)WebRequest.Create("http://mmsc.monternet.com");
                                                            httpReq.KeepAlive = false;
                httpReq.Proxy = new WebProxy("http://10.0.0.172:80");
                httpReq.Method = "POST";
                httpReq.Timeout = Timeout.Infinite;
           httpReq.Accept= "application/vnd.wap.mms-message,text/*,*/*";
         
                httpReq.Headers.Add("Accept-Charset","iso-8859-1, utf-8, iso-10646-ucs-2; q=0.6");
                httpReq.ContentType = "application/vnd.wap.mms-message";

                // Write Post Dat
                httpReq.ContentLength = mms_length;
                Stream sReq = httpReq.GetRequestStream();
                                                            sReq.Write(tmp,0,tmp.Length);
                sReq.Close();

                // Get Response
                HttpWebResponse httpRsp = (HttpWebResponse)httpReq.GetResponse();//就在这里出错
                Stream stream_Response = httpRsp.GetResponseStream();
                StreamReader sReader = new StreamReader(stream_Response,Encoding.ASCII);
                string str = sReader.ReadToEnd();
                sReader.Close();
                stream_Response.Close();
                httpRsp.Close();
                //httpReq.Abort();
                MessageBox.Show(str);
            }
            catch(InvalidOperationException ee)
            {
                MessageBox.Show("IN one:" + ee.Message);
            }


说明：我是通过代理向移动MMSC发送彩信，10.0.0.172：80是CMWAP网关。http://mmsc.monternet.com是MMSC的URL